1. The Field of the Invention
This invention relates to devices for selectively attaching a fixture to the exterior of an elongated member of circular cross-section, such as a length of medical tubing. More specifically, the invention pertains to a connector for effecting a fluid-tight termination of the outer lumen of a coaxial lumen tube assembly against the inner lumen tube of that assembly. The invention has particular utility at the proximal end of a coaxial lumen tube assembly used with an implanted extrapulmonary blood gas exchange device to enable that device to communicate with extracorporeal support equipment.
2. BACKGROUND ART
Disclosed in U.S. Pat. Nos. 4,583,969 and 4,850,958 are methods an apparatus for the in vivo oxygenation of blood without using or disturbing the lungs of the patient. A longitudinal bundle of elongated, gas-permeable capillary tubes bound are together at the ends and inserted into the vena cava through an incision made at a remote site in the circulatory system, such as the femoral or iliac vein.
In the embodiment of the apparatus disclosed in U.S. Pat. No. 4,850,958, a coaxial lumen tube assembly is used to establish the inward and outward gas flow required between extracorporeal support equipment and the implanted bundle. A feed gas, rich in oxygen, is supplied through one lumen of the coaxial lumen tube assembly to the proximal end of the bundle of capillary tubes. The feed gas passes through the capillary tubes and is exchanged through the walls thereof for metabolic byproducts in the blood circulating in the aorta about the exterior of the capillary tubes. At the distal ends of the capillary tubes, the gas is removed through the other lumen of the coaxial lumen tube assembly. In the particular embodiment of the apparatus disclosed, fresh oxygen-bearing feed gas is supplied to the implanted device through the central lumen of the coaxial lumen tube assembly, while exhausted gas is removed through the surrounding outer lumen.
Outside of the body of the patient, the inner and outer lumen tubes of the coaxial lumen tube assembly must become separated, to permit their connection individually to different equipment. The inner lumen tube is connected to a source of the pressurized feed gas; the outer lumen is connected to a vacuum. At a point where the flow paths of the coaxial lumen tube assembly branch, it is necessary to terminate the outer lumen tube in a fluid-tight seal against the inner lumen tube. In the past, efforts to effect these functions at the branching point of the two flow paths has focused without full success on various Y-connector configurations. The constraints on such Y-connectors imposed by the surgical procedures associated with the implantation and use of the blood gas exchange device have resulted in structural demands which have yet to be satisfied.
It is necessary, for example, during the implantation procedure of the blood gas exchange device for the proximal terminus of the outer lumen of the dual-lumen assembly to be free of any Y-connector. After implantation is complete, the Y-connector is slid down the inner lumen tube to the proximal terminus of the outer lumen tube and secured in place. The sealing engagement between the Y-connector and the outer lumen tube may be effected by a number of known structures. The required slidable sealing engagement between the Y-connector and the inner lumen tube has, by contrast, presented a challenge to achieve.
In order to effect a fluid-tight seal by which to terminate the outer lumen tube against the inner lumen tube, it is necessary to effect an unbroken contact about the entire circumference of the outer surface of the inner lumen tube. To do so, a structure is required that will impose radially directed forces against the exterior of the inner lumen tube in a manner that is circumferentially uniform. If the radial forces are not circumferentially uniform, grave consequences may result. The fluid-tight seal may be compromised, or the shape of the inner lumen tube may become distorted, leading to crimping and constricted fluid flow.
The desired fluid-tight seal must be capable of being repeatedly applied and released. The fact that the seal imposed must be released and reapplied only serves to emphasize the need to develop radially directed forces against the exterior of the inner lumen tube which are circumferentially uniform. If the shape of the inner lumen tube is distorted by the application of these forces, an acceptable seal might result in the first instance. Nevertheless, after the release of the seal and its reapplication, possibly at a different longitudinal location or in a manner radially displaced from the initial application, a secure seal will be difficult to guarantee. Furthermore, the sealing elements involved must be both resilient and extremely durable. Thus, the sealing force to be effected must be capable of repeated actuation without degrading the structural integrity of the Y-connection or the inner lumen tube.
The Y-connector seal must also be one that releases only when intended. Accidental or creeping release of the seal, such as occurs in prior devices that secure the seal using threaded fittings, are undesirable. On the other hand, the seal must be capable of rapid and certain disengagement.
Finally, it is of concern that the coupling mechanisms associated with the Y-connector be easily assemblable, that the Y-connector be repeatedly slidable over the inner lumen tube without damage to either component, and that the manner of operating the mechanisms associated with the Y-connector be unambiguous to surgical personnel.
In the broader context, the problem of effecting a fluid-tight seal in the context just described is the problem of providing a connector for effecting the selective, reliable, and reversible attachment of a fitting to the exterior of an elongated member of circular cross-section. Where the elongated member is a length of medical tubing, the apparatus for effecting the desired connection must embody a combination of firm, yet not overpowering, compressive forces. Once this balance has been achieved, the compressive forces can be utilized on behalf of a fluid-tight seal or merely a mechanical attachment, as for example with the attachment to an I.V. tube of a label, a monitor, or a reserve piece of equipment.
In the context of an in vivo extrapulmonary blood gas exchange device, such as that described in U.S. Pat. No. 4,850,958, the general principles by which such an object is achieved take on specific detailed form. While that specific detailed form will be disclosed hereafter in a discussion of the invention, it should be understood that the principles embodied therein have a wide range of applicability without departing from the broad insights that constitute that invention.